Heretofore, there have been many designs for devices to pick up an object utilizing a suction tube with an applied vacuum. In general, such vacuum pickup devices have been designed with an open ended cylinder having a nozzle surface which seals to the object to accomplish the physical attachment. However, the nozzle of the vacuum pickup device is generally lacking any means to locate or position the object onto a vacuum nozzle and thereby requires the utilization of sophisticated alignment monitors and location/position correction capabilities.
A further problem arises in the use of traditional pick-up nozzles for holding and transferring very small components. This problem is exacerbated when components such as die on a microscopic scale must be handled. Moreover, when such components must be passed between vacuum nozzles, a cumulative positioning error may be generated. Or, as is sometimes the case, the component or die is lost altogether as it was being transferred between nozzles.
As used herein the term “die,” or more specifically microscopic die, is intended to include various electrical, electromechanical, mechanical or other components, and particularly includes those that may be formed through a wafer processing technique and subsequently separated into discrete components. As such, die are not limited to semiconductor components, but may be any similar devices such as mirrors, micro-electro-mechanical systems (MEMS), micro-optical electrical module (MOEM) which are formed there upon a wafer and presented in the same manner as semiconductor components. Furthermore, a die contained on a wafer may include post processing features such as, but not limited to, chip scale packaging (CSP), wafer level processing (WLP) as well as passivation and underfill layers.
Pick-up vacuum nozzles currently utilized in automated assembly equipment for picking up and moving larger die from a source to a destination are often ineffective for reliably maintaining the aspect and relative position of smaller, microscopic die. For example, in assembling printed circuit boards, bare die are acquired from a wafer by a pick nozzle contained in a die feeder and are subsequently transferred to a pick-up location. The traditional pick nozzle is connected to a vacuum source which may be actuated by any of a number of devices, including a pneumatic valve. The pick nozzle is extended to contact the wafer at which time vacuum is applied to the nozzle and in turn a bare die is acquired and securely captured by the nozzle. The pick nozzle is often associated with a mechanism to turn the die over along an axis parallel to the plane of the wafer and is then moved into position to be received by yet another nozzle for subsequent delivery to a circuit or printed wiring board assembly machine.
In one such embodiment an intervening nozzle is used to accommodate the turning over of the die prior to being transferred onto the presentation nozzle for delivery to the assembly machine. This additional die transfer operation is implemented when the die is to be placed circuit side down onto the board or substrate; this is commonly referred to in the art as a “flip chip” component, where the circuits on the die face align with the printed circuits on the board. In the alternative, the die is presented with the circuit facing away from the printed circuit board (PCB) and is electrically interconnected with fine wires that are subsequently bonded between pads on the PCB and the die.
While the die is being transitioned between a pair of nozzles it is necessary to maintain the position of the die within the centerline of the feed path. Once the nozzles are in contact with opposing surfaces of the die, the vacuum is released from one and applied to the other, thus passing the holding control of the die therebetween with minimal, if any, control of the x, y locations or angular orientation (theta) relative to a nozzle. Furthermore, in order to facilitate a rapid hand-off of the die, it is often necessary to overcome an inherent hysteresis within the nozzle pneumatics, as well as the natural die adhesion to the nozzle tip. Accordingly, in order to accelerate the transfer of a die in a high speed circuit board assembly systems, the holding vacuum is switched to a positive air pressure to release, or “blow”, the die off the releasing nozzle. Generally a settling time delay is employed before the die transfer is completed, in order to settle the turbulent air around the die before the nozzles are retracted.
However, in the handling of microscopic die having a minuscule mass and surface area, the aerodynamic performance of the die is highly unpredictable—even when the die is in simultaneous contact with the nozzles. The possibility of a disturbance of die alignment, particularly as a result of turbulent air flow created by the blow-off step described above, becomes a significant limitation. Unfortunately, the obvious solution of increasing the “settling” time delay is not practical due to the negative impact on the throughput of such systems (measured in die/sec). Furthermore, with the introduction of a die having a surface area of about 0.25 mm2 or less, the vacuum holding force is minimal at transfer, and often results in the die becoming displaced from the center line of the nozzle at the time the vacuum is switched to pressure. In the case where the die becomes dislocated on the nozzle tip a vacuum seal might not occur relative to the receiving nozzle, thereby compromising the control of the die and resulting in the potential for the die being dropped or mishandled.